Does Lower Extremity Ultrasound Have a Role in Ruling Out PE?
Ans: Ultrasound is not necessary when computed tomography is performed.
The role of venous duplex ultrasound (US) of the legs in patients with suspected pulmonary embolism (PE) is not clear with the advent of D-dimer testing and computed tomography (CT) pulmonary angiography. European researchers prospectively randomized 1819 consecutive outpatients with suspected PE to one of two diagnostic strategies: D-dimer measurement plus chest CT (if D-dimer level is >500 ng/mL; DD-CT) or D-dimer measurement plus bilateral lower extremity venous compression US (if D-dimer level is >500 ng/mL), followed by chest CT if US results are negative (DD-US-CT). Nine percent of patients in the DD-US-CT group did not undergo CT because deep venous thrombosis (DVT) was detected on US, and treatment was started without further testing.
The prevalence of PE was 20.6% in both groups. Overall, 126 patients were excluded from the analysis because they were not treated according to protocol. Rates of adverse events were similar in both treatment groups. Among patients in both groups in whom PE was excluded based on negative CT results, risk for PE at 3-month follow-up was similar in the two groups (0.3%). The number of lower extremity US exams that would need to be performed to avoid one chest CT study was 11 (number needed to treat). Mean direct costs per patient were 24% lower in the DD-CT group than in the DD-US-CT group. The authors conclude that lower extremity US is not necessary for ruling out PE when CT is used.
Comment: This noninferiority study supports the widely used strategy of performing D-dimer testing and CT scanning to exclude PE, without performing lower extremity US. However, in patients with clinical findings suggestive of lower extremity DVT, venous compression US might avoid the need for CT. Furthermore, contraindications to CT limit its usefulness; in this study, 32% of screened patients were excluded because of intravenous contrast allergy, renal failure, or other contraindications. For such patients, venous compression US of the legs remains a valuable test.
— Kristi L. Koenig, MD, FACEP
Published in Journal Watch Emergency Medicine May 9, 2008
Citation(s): Righini M et al. Diagnosis of pulmonary embolism by multidetector CT alone or combined with venous ultrasonography of the leg: A randomised non-inferiority trial. Lancet 2008 Apr 19; 371:1343.